Cooling system with adjustable internal heat exchanger

ABSTRACT

A cooling system includes: connected in a loop by fluid lines and in succession, a compressor, a condenser, an expansion valve, and an evaporator; and an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, the first conduit being part of the fluid line between the condenser and the expansion valve and the second conduit being part of the fluid line between the evaporator and the compressor. A bypass fluid line is arranged between two ends of the first conduit of the internal heat exchanger or extends between one of the two ends of the first conduit and a position along a length of the first conduit.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2017/064200, filed on Jun. 9,2017, and claims benefit to British Patent Application No. GB 1610120.6,filed on Jun. 10, 2016. The International Application was published inEnglish on Dec. 14, 2017 as WO 2017/212058 under PCT Article 21(2).

FIELD

The invention relates to a cooling system comprising, connected in aloop by fluid lines and in succession, a compressor, a condenser, anexpansion valve and an evaporator, further comprising an internal heatexchanger having a first conduit in heat exchanging contact with asecond conduit, wherein the first conduit is part of the fluid linebetween the condenser and the expansion valve and wherein the secondconduit is part of the fluid line between the evaporator and thecompressor.

BACKGROUND

Such a cooling system is for example known from EP 1043550. Thispublication describes a cooling system in which a fluid, in particularCO2 is used, which is made super-critical in the high pressure linebetween the compressor and the expansion valve. Due to the coolingeffect of the condenser, the pressure in the high pressure line couldvary. Especially, dependent on the ambient temperature. In cold weather,the fluid in the high pressure line would be cooled down to a far lowertemperature, than in hot weather. This results in a different pressurein the high pressure line depending on the ambient temperature. Thischange in pressure has an adverse effect on the COP (coefficient ofperformance) of the cooling cycle.

EP 1043550 proposes to provide a bypass channel around the low-pressureline of the internal heat exchanger, i.e. between the evaporator and thecompressor. The bypass channel is provided with a controllable valve,which is controlled based on the pressure in the high pressure line toensure, that the fluid, in particular CO2, is kept at the optimalpressure. So, if the pressure rises in the high pressure line, thebypass channel is closed, such that the fluid in the high pressure linecan be cooled down with the internal heat exchanger and accordinglylower the pressure in the high pressure line. On the other hand, if thepressure falls, the bypass channel is opened, such that the fluid in thehigh pressure line is not cooled further by the internal heat exchangerresulting in a higher pressure.

An internal heat exchanger (IHX) exchanges heat between the warm highpressure side and the cold suction side. Generally, the usage of aninternal heat exchanger in a refrigeration cycle has a positive effecton mainly two physical values, the cooling capacity and the systemefficiency (COP). The cooling capacity is mainly influenced by twofactors, the refrigerant mass flow and the enthalpy difference in theevaporator.

The enthalpy difference is influenced by the cool down of therefrigerant on the high pressure side of the internal heat exchanger.The lower the temperature of the refrigerant at the high pressure sideoutlet of the IHX the bigger is the enthalpy difference in theevaporator, leading to increasing cooling capacity. At the suction sideof IHX the refrigerant is heated up and dries out (drop lets of liquidrefrigerant are evaporated in the IHX). This dry out has a positiveeffect on the compressor since the power consumption goes down. Thisadditionally leads to a better COP value.

An additional potential positive effect is that the overheating of theevaporator could be partly moved into the IHX which enables the use of alarger portion of the evaporator surface for air cooling instead ofoverheating the refrigerant. In summary: The higher the available IHXheat transfer capacity would be the better the above mentioned positiveeffects could be exploited. This would help to provide better coolingcapacity and a higher COP of the entire AC system.

However, increasing the IHX performance is limited by the maximumallowable gas temperature on the suction side of the compressor. Thereason is that a higher suction side temperature increases the operatingtemperature in the compressor and as a consequence also the dischargetemperature. The maximum allowable operating temperature is specified bycompressor manufacturers and is the limiting factor. Therefore, themaximum compressor temperature is also limiting the maximum possible IHXperformance.

Also the IHX performance of the base system is not flexible, IHX length,geometry and material are factors which determine the heat exchangecapacity. These factors are fixed, but to provide optimal AC systemperformance in all changeable environments and drive conditions and alsofor different refrigerants used in one system (R134a/HFO1234yf)adaptable performance of the IHX is required.

SUMMARY

In an embodiment, the present invention provides a cooling system,comprising: connected in a loop by fluid lines and in succession, acompressor, a condenser, an expansion valve, and an evaporator; and aninternal heat exchanger having a first conduit in heat exchangingcontact with a second conduit, the first conduit being part of the fluidline between the condenser and the expansion valve and the secondconduit being part of the fluid line between the evaporator and thecompressor, wherein a bypass fluid line is arranged between two ends ofthe first conduit of the internal heat exchanger or extends between oneof the two ends of the first conduit and a position along a length ofthe first conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in even greater detail belowbased on the exemplary figures. The invention is not limited to theexemplary embodiments. Other features and advantages of variousembodiments of the present invention will become apparent by reading thefollowing detailed description with reference to the attached drawingswhich illustrate the following:

FIG. 1 shows a schematic view of a first embodiment of a cooling systemaccording to the invention.

FIG. 2 shows a schematic view of a second embodiment of a cooling systemaccording to the invention.

FIG. 3 shows a schematic view of a third embodiment of a cooling systemaccording to the invention.

FIG. 4 shows a schematic view of a fourth embodiment of a cooling systemaccording to the invention.

FIGS. 5a and 5b show a schematic view of a two diagrams governing apreferred embodiment of the method for controlling a cooling systemaccording to the invention.

DETAILED DESCRIPTION

In an embodiment, the present invention reduces the above mentioneddisadvantages.

In an embodiment, the present invention provides a cooling system, whichcooling system is characterized in that a bypass fluid line arrangedbetween the two ends of the first conduit of the internal heatexchanger.

Providing the bypass fluid line between the two ends of the firstconduit and therefore in the high pressure or liquid line of the coolingsystem, allows for a direct control of the heat exchange in the IHX.

It also provides for the advantage that the pressure drop is limited.There is no significant pressure drop because of low flow speed ofrefrigerant in its liquid phase. With a bypass on the suction side, asknown in the prior art, there is a risk of pressure drop due to bypasscomponents and a corresponding negative impact on whole system.

The hose diameters on the liquid side of the system are smaller than onthe suction side, therefore allowing for a more compact (smaller, hose,valve and more compact connectors) arrangement of the invention, forexample in the engine compartment of a vehicle. This also results inlower production costs.

The invention has further the advantage, that it has no negative impacton noise, vibration, and harshness (NVH) behavior. Compared to a bypasssolution on the suction side, the flow noise in a system according tothe invention will not increase. The NVH behavior is already critical inconventional AC systems, because the evaporator often acts as a loudspeaker.

With the invention, there is also no risk of oil accumulation. The oiltransport through the cooling system is ensured by avoiding to create socalled oil pockets since the oil is dissolved in the liquid. In theprior art, this is way more critical on the suction side where therefrigerant is in vapor phase. In such a case, the oil is typicallyswept along with the gas-phase refrigerant—a sufficient flow speed needsto be ensured, which would be at risk with a suction-side bypasssolution.

Furthermore, a liquid phase bypass, as provided by the invention, offersimproved flow control compared to a gas-phase (faster and turbulentflow) bypass, as known in the prior art, due to the lower flow speed (ofthe liquid) and more constant conditions.

In case an internal heat exchanger is used, a by-pass can more easily bearranged and with a limited number of modifications, because the liquidside in the internal heat exchanger is typically the outside tube. Thisallows for example for connection of the by-pass channel along thelength of the liquid line of the internal heat exchanger to provide apartial by-pass. Thus a bypass can easily be added where needed.

EP 1043550 discloses a method by controlling the heat transfer of theIHX by providing a bypass channel in the low pressure or suction line.With the bypass channel, the heat transfer of the IHX can be managed tocontrol the pressure in the high pressure line.

As EP 1043550 requires that the pressure in the high pressure or liquidline is kept constant, a bypass channel cannot be provided in the highpressure line, as this would influence the pressure, when the bypasschannel is opened or closed.

Therefore, EP 1043550 provides a bypass channel in the low pressureline, such that the heat exchange of the IHX is influenced, while thepressure in the high pressure line is not influenced directly by openingor closing the bypass channel. This is also the result of the state ofthe fluid in the low pressure line, which fluid has the gaseous state.The gaseous can easily be compressed, such that any influences ofopening or closing the bypass channel has no substantial effect on thepressure in the low pressure line, let alone the pressure in the highpressure line.

With the invention, the bypass channel is arranged in the high pressureline, in which the fluid is liquid and provides easy control of theamount of liquid flowing through the IHX and through the bypass. So,although the pressure in the high pressure line may fluctuate, thecontrol of the IHX is more direct with the bypass channel in the highpressure line, resulting in a better control of the temperature on thesuction side of the compressor and according results in a longerlifespan of the compressor, while optimizing the COP.

A preferred embodiment of the cooling system according to the inventionfurther comprises a controllable valve arranged in the bypass fluid linefor controlling the amount of fluid flowing through the bypass fluidline. This amount of fluid flowing through the bypass fluid line andtherefore not flowing through the IHX depends on the necessary amount ofheat exchange needed for an optimal cooling system performance. In apreferred embodiment the controllable valve is a two way valve. In afurther embodiment the controllable valve is a proportional valve. In afurther embodiment the controllable valve is a proportional three wayvalve.

In a further embodiment of the cooling system according to the inventionthe controllable valve is a three way valve and is arranged either atthe junction of the bypass fluid line and the fluid line between thecondenser and the internal heat exchanger (inlet junction) or at thejunction of the bypass fluid line and the fluid line between theinternal heat exchanger and the expansion valve (outlet junction).

With the three way valve there is direct control possible of the amountof refrigerant flowing through the bypass line and the heat exchanger.If a two way valve is used in the bypass fluid line, then changingresistance in the internal heat exchanger will influence the ratio ofthe amount flowing through the bypass line and the internal heatexchanger.

A preferred embodiment of the cooling system according to the invention,further comprises a temperature sensor arranged in the fluid linebetween the compressor and the first conduit of the internal heatexchanger for controlling the controllable valve based on thetemperature measured by the temperature sensor.

By continuously measuring the refrigerant temperature on the dischargeline, i.e. the fluid line between the compressor and condenser, andcorresponding control of the by-pass valve, it is possible to provideoptimal IHX performance in all changeable environments and driveconditions, wherein the compressor is protected against overheating.

The coupling between the temperature sensor and the controllable valvecould be a direct connection, using a thermostatically control. This isa mechanical connection, wherein typically a gas, expanding in thetemperature sensor part is used to mechanically control a valve.However, it is preferred to have an electronic controller coupling thecontrollable valve and the temperature sensor, as this provides for moreflexibility in the control strategy.

In a further preferred embodiment the temperature sensor arranged in thefluid line between the compressor and the first conduit of the internalheat exchanger is arranged between the compressor and the condenser,preferably directly after the compressor.

A further preferred embodiment of the cooling system according to theinvention further comprises a temperature sensor arranged in the fluidline between the second conduit of the internal heat exchanger and thecompressor and a control device connected to the temperature sensor andthe controllable valve, for controlling the controllable valve based onthe temperature measured by the temperature sensor.

Preferably, the cooling system further comprises a pressure sensorarranged in the fluid line between the second conduit of the internalheat exchanger and the compressor.

By both measuring the temperature and the pressure on the suction sideof the compressor, it is possible to ensure that only gaseousrefrigerant enters the compressor. This in turn allows for thesuperheating of the refrigerant, which typically is done in theevaporator, to be done in the internal heat exchanger. This enables thefull capacity of the evaporator to be used for cooling air, while theinternal heat exchanger will ensure the superheating of the refrigerantand accordingly ensure that only gaseous refrigerant enters thecompressor.

In yet another embodiment also the expansion valve is controllable, suchthat all aspects of the cooling system can be controlled and optimalsettings can be chosen depending on the circumstances.

In a preferred embodiment the cooling system filled with R134a orHFO1234yf as refrigerant. In a further preferred embodiment the coolingsystem is free of CO2.

In a further embodiment the fluid line between the condenser and thefirst conduit of the internal heat exchanger is permanently open.

In a further embodiment the bypass fluid line contains only a singlecontrollable valve and/or the amount of fluid flowing through the bypassfluid line is controlled via a single controllable valve.

In a preferred embodiment the smallest diameter of the fluid linebetween the inlet junction and the first conduit of the internal heatexchanger can be larger than the largest diameter of the bypass fluidline. This has the advantage that the bypass fluid line can bedimensioned smaller, which saves cost.

In an alternative embodiment the smallest diameter of the bypass fluidline is larger than the largest diameter of the fluid line between theinlet junction and the first conduit of the internal heat exchanger.

In a further preferred embodiment the condenser is free of a branch-off.Preferably, the condenser comprises exactly one inlet and exactly oneoutlet. In a further preferred embodiment the first conduit of theinternal heat exchanger and the expansion valve are connected solely viaa single fluid line.

In a further preferred embodiment the controllable valve is integratedin a connecting flange of the internal heat exchanger.

In a further preferred embodiment the cooling system is free of anysensor in a fluid line between the condenser and the internal heatexchanger.

In an embodiment, the invention provides a method for controlling acooling system according embodiments described above, comprising thesteps:

-   -   measuring, preferably continuously, a fluid temperature of a        refrigerant of the cooling system using a temperature sensor        comprised by a fluid line between the compressor and the        condenser, wherein the temperature sensor is preferably located        close to or directly at the outlet side of the compressor,    -   controlling, proportionally to the fluid temperature measured by        the temperature sensor, a mass flow of fluid passing through the        internal heat exchanger by automatically actuating a        controllable valve that is arranged to control the amount of        fluid flowing through the bypass fluid line.

In a preferred embodiment the method includes the step:

-   -   beginning to proportionally reduce the mass flow of fluid        passing through the internal heat exchanger by automatically        actuating the controllable valve that is arranged to control the        amount of fluid flowing through the bypass fluid line and        corresponding, if the measured temperature after the compressor        is shortly before exceeding a predefined temperature threshold        or range and thereby reducing the heat exchange in the internal        heat exchanger.

Preferably the control is designed such that no unsteady change in heatexchange occurs.

In a In an even further preferred embodiment the method includes thestep:

-   -   beginning to proportionally increase the mass flow of fluid        passing through the internal heat exchanger by automatically        actuating the controllable valve that is arranged to control the        amount of fluid flowing through the bypass fluid line and        corresponding, if the measured temperature after the compressor        starts to fall below the predefined temperature threshold or        range and thereby increasing the heat exchange in the internal        heat exchanger.

In a further preferred embodiment the method includes the steps:

-   -   measuring, preferably continuously, the fluid temperature and        the pressure of the refrigerant of the cooling system using a        further temperature sensor and a pressure sensor both of which        are comprised by a fluid line between the second conduit of the        internal heat exchanger and the compressor, wherein the further        temperature sensor and the pressure sensor are preferably        located close to or directly at the inlet side of the        compressor;    -   continuously determining or calculating, based on the        measurements of the further temperature sensor and a pressure        sensor and using a controller, an overheating of the fluid;

In a further preferred embodiment the method includes the step:

-   -   proportionally increasing the fluid mass flow through the bypass        fluid line if the overheating of the fluid exceeds or is about        to exceed a predefined overheating max overheating threshold or        overheating range

In a further preferred embodiment the method includes the step:

-   -   proportionally reducing the fluid mass flow through the bypass        fluid line if the overheating of the fluid falls or is about to        fall below the predefined max overheating threshold or        overheating range.

In a further preferred embodiment the method includes the step:

-   -   keeping the mass flow through the bypass fluid line steady close        or equal to zero, if the continuously determined or calculated        overheating remains on the predefined optimal overheating        threshold or within the predefined overheating range.

FIG. 1 shows schematically a cooling system 1 comprising, connected in aloop by fluid lines and in succession, a compressor 2, a condenser 3, anexpansion valve 4 and an evaporator 5.

To further improve the cooling system 1, an internal heat exchanger 6 isprovided with a first conduit 7 arranged in the line 8, 9 between thecondenser 3 and the expansion valve 4, and a second conduit 10 arrangedin the line 11, 12 between the evaporator 5 and the compressor 2.

Furthermore, a bypass fluid line 13 with a controllable valve 14 isarranged between the line 8 and line 9, i.e. between the two ends of thefirst conduit 7 of the internal heat exchanger 6. The bypass fluid line13 is arranged between an inlet junction 28 and an outlet junction 29.

The fluid line 8 between the condenser 3 and the first conduit 7 of theinternal heat exchanger 6 is permanently open. The first conduit 7 ofthe internal heat exchanger 6 and the expansion valve 4 are connectedsolely via the single fluid line 9.

A temperature sensor 23 is arranged in the fluid line 17 between thecompressor 2 and the condenser 3 to measure the discharge temperature ofthe refrigerant exiting the compressor 2. The temperature sensor 23 isarranged between the compressor 2 and the condenser 3 close to thecompressor 2.

Both the controllable valve 14 and the temperature sensor 23 areconnected to a controller 16, such that the controllable valve 14 can becontrolled based on the measured temperature in the fluid line 17.

As can be seen from FIG. 1, the bypass fluid line 13 contains only asingle valve, that is the controllable valve 14. The amount of fluidflowing through the bypass fluid line 13 is controlled only via thissingle controllable valve 14.

The controllable valve 14 is a two way proportional valve. If thecontrollable valve 14 is closed (0% position) no fluid passes throughthe bypass fluid line 13. The smallest diameter of the bypass fluid line13 is larger than the largest diameter of the fluid line 8, 9 betweenthe inlet junction 28 and the outlet junction via the first conduit 7 ok

The fluid line 8 between the condenser 3 and the inlet junction 28 aswell the fluid line 9 between the outlet junction 29 and the expansionvalve is sufficiently large in diameter to transport the combined massof fluid through the bypass fluid line 13 and the first conduit.

Therefore, if the controllable valve 14 is maximum open (100% position),the largest share of the fluid exiting the condenser 3 passes throughthe bypass fluid line.

Alternatively or additionally to designing the fluid line 8, 9 betweenthe inlet junction 28 and the outlet junction via the first conduit 7comparatively smaller in diameter, a slight pressure drop via the firstconduit 7 can be achieved by placing a throttle on the inlet or outletside of the first conduit 7, e.g. in a connecting flange 26 of theinternal heat exchanger (see FIG. 6).

In the exemplary embodiment shown in FIG. 1 the bypass fluid line 13 isembodied by a pipe with about (for example) 10 mm diameter, while fluidline 8 is embodied by a pipe with about (for example) 8 mm diameter.Other diameters are possible.

With the temperature sensor arranged in the high pressure line 17directly after the compressor 2, the discharge temperature can becontrolled and accordingly allows for protecting the compressor 2against overheating. The discharge temperature is influenced by thesuction temperature, the compressor rpm and the power consumed by thecompressor. So, also with this temperature sensor 23 being arrangedafter the compressor 2, the compressor can be protected and the heatexchange capacity can be maximized and optimized.

FIG. 2 shows a second embodiment 20 of a cooling system according to theinvention. The cooling system 20 is similar to the cooling system 1 ofFIG. 1 and the same parts are referenced by the same reference signs.

In the embodiment 20, the bypass fluid line 13 is provided at thejunction of the fluid line 8 and the bypass line 13 with a controllablevalve 22. This provides for a better fluid control and allows for adirect control of the amount of refrigerant flowing through the bypassline 13 and the first fluid line 7 of the heat exchanger 6.

Furthermore, the embodiment 20 comprises a second temperature sensor 15arranged in the line 12 between the internal heat exchanger 6 and thecompressor 2. Also a pressure sensor 25 is arranged in the line 12between the internal heat exchanger 6 and the compressor 2. The secondtemperature sensor 15 and the pressure sensor 25 are arranged directlyor close at/to the inlet side of the compressor 2.

These additional sensors 15 and 25 provide for an improved control incomparison to the embodiment of FIG. 1 allowing for maximal optimizationof the cooling system performance.

The pressure value measured by the sensor 25, in combination with thetemperature, measured by the temperature sensor 15, in this line 12, canbe used to control the ideal refrigerant overheating before thecompressor 2. This provides for a higher COP and compressor protection,while making the partial outsourcing of refrigerant overheating from theevaporator 5 into the IHX 6 possible.

The use of a temperature sensor 15, a temperature sensor just after thecompressor 2 and a pressure sensor in the line 12, can be combined inany configuration desired to provide optimal controllability and maximalpossible optimization of the cooling system performance.

FIG. 3 shows a schematic view of a third embodiment of a cooling systemaccording to the invention. This embodiment 30 is almost identical tothe embodiment 20 as shown in FIG. 2.

The difference is the arrangement of the bypass fluid line 13, which notfully extends between the line 8 and line 9, i.e. between the two endsof the first conduit 7 of the internal heat exchanger 6. In thisembodiment 30, however, the bypass fluid line extends from the line 8 toa position along the length of the first conduit 7 of the internal heatexchanger 6. This provides a partial bypass fluid line 13.

As can be seen from FIGS. 2 and 3, the amount of fluid flowing throughthe bypass fluid line 13 is controlled only via a single controllablevalve 22, which is a three way proportional valve defining the inletjunction 28.

FIG. 4 shows schematically a cooling system 1 comprising, connected in aloop by fluid lines and in succession, a compressor 2, a condenser 3, anexpansion valve 4 and an evaporator 5.

To further improve the cooling system 1, an internal heat exchanger 6 isprovided with a first conduit 7 arranged in the line 8, 9 between thecondenser 3 and the expansion valve 4, and a second conduit 10 arrangedin the line 11, 12 between the evaporator 5 and the compressor 2.

Furthermore, a bypass fluid line 13 is arranged between the line 8 andline 9, i.e. between the two ends of the first conduit 7 of the internalheat exchanger 6. The first conduit 7 of the internal heat exchanger 6and the expansion valve 4 are connected solely via the single fluid line9.

The controllable valve 14 in form of a proportional two way valve isplaced, preferably directly, at the input side of the first conduit 7 ofthe internal heat exchanger 6. Alternatively (shown dotted) acontrollable valve 14′ can be placed, preferably directly, at the outputside of the first conduit 7 of the internal heat exchanger 6.

A temperature sensor 23 is arranged in the fluid line 17 between thecompressor 2 and the condenser 3 to measure the discharge temperature ofthe refrigerant exiting the compressor 2. The temperature sensor 23 isarranged between the compressor 2 and the condenser 3 directly after(and close to the outlet of) the compressor 2.

Both the controllable valve 14 and the temperature sensor 23 areconnected to a controller 16, such that the controllable valve 14 can becontrolled based on the measured temperature in the fluid line 17.

As can be seen from FIG. 4 the amount of fluid flowing through the IHXline 7 is controlled only via this single controllable valve 14.

The controllable valve 14 is a two way proportional valve. If thecontrollable valve 14 is closed (0% position) all fluid from thecondenser 3 passes through the bypass fluid line 13.

In the embodiment of FIG. 4, the diameter of the bypass fluid line 13,i.e. between inlet junction 28 and outlet junction 29 is smaller thanthe diameter of fluid lines 8, 9 between the inlet junction 28 and theoutlet junction 29 via the first conduit 7.

Therefore, if the controllable valve 14 is maximum open (100% position),the largest share (almost 100%) of the fluid exiting the condenser 3passes through the first conduit 7 of the internal heat exchanger 6.

In the embodiment of FIG. 4 the controllable valve 14 is, by way ofexample, integrated in a connecting flange 26 on the inlet side of theinternal heat exchanger 6. Alternatively the controllable valve 14 canbe placed in the fluid line 8 between the inlet junction 28 and thefirst conduit 7, or (shown dotted) controllable valve 14 can be placedin in the fluid line 9 between the outlet junction 29 and the firstconduit 7.

In the embodiment shown in FIG. 4 the bypass fluid line 13 is embodiedby a pipe with about (for example) 6 mm diameter, while fluid line 8 isembodied by a pipe with about 8 mm diameter. Other diameters arepossible.

FIG. 5 shows a schematic view of a two diagrams governing a preferredembodiment of the method for controlling a cooling system cooling systemaccording to the invention. By way of example FIG. 5 refers to thecooling system 20 of FIG. 2.

The vertical axis of diagram a) denotes the mass flow of fluid throughbypass fluid line 13, while the horizontal axis of diagram a) denotesthe temperature measures by temperature sensor 23 on the outlet side ofcompressor 2. Thus, diagram a) refers to a first control loop.

The vertical axis of diagram b) denotes the mass flow of fluid throughbypass fluid line 13, while the horizontal axis of diagram b) denotesthe overheating determined based on the measurements of the furthertemperature sensor 25 and the pressure sensor 15 on the inlet side ofcompressor 2. Thus, diagram a) refers to a second control loop.

Diagram a)

A fluid temperature of a refrigerant of the cooling system 20 ismeasured continuously using the temperature sensor 23 comprised by afluid line 17 between the compressor 2 and the condenser 3. Thetemperature sensor 23 is located close to the outlet side of thecompressor 2.

Proportionally to the fluid temperature measured by the temperaturesensor 25, a mass flow of fluid passing through the internal heat 6exchanger is controlled by automatically and proportionally actuatingthe controllable valve 22 that is arranged to control the amount offluid flowing through the bypass fluid line 13.

In diagram 5 a) the measured temperature T1 after the compressor is, forexample, shortly before exceeding a predefined range R1 (indicated bysolid arrow A1). Therefore the mass flow of fluid passing through theinternal heat exchanger 6 is reduced by automatically actuating thecontrollable valve 22. Thus, the mass flow through bypass fluid line 13increases as can be seen from the diagram.

Thereby the heat exchange in the internal heat exchanger 6 is decreased,which keeps T1 in the desired range R1 (indicated by dotted arrow A1′).

The desired range R1 extends in the example from 80% Tmax (maximumtemperature at the outlet side of compressor 2) to Tmax. Alternatively,for example, the desired range R1 could extend from 60% Tmax to Tmax. Ofcourse, the range R1 can be adapted to a specific cooling system. Tmaxcan be, for example, 100° C. or 150° C. or in between.

Even though it is generally desirable to keep temperature at the outletside of compressor 2 as low as possible, the first control loop allowsfor a maximum thermal utilization of the internal heat exchanger 6 inthe sense that it allows to operate it safely in a region close to Tmax.In other operating points of the cooling system measured temperature T2after the compressor 2 may be below 50% Tmax. In this case the flowthrough the bypass fluid line 13 can be zero. Thus, it becomes apparentthat the first control loop acts as a first safety loop.

If, however, a measured temperature T2 after the compressor is, forexample, shortly before falling below the predefined range R1 (indicatedby solid arrow A2), the mass flow of fluid passing through the internalheat exchanger 6 is increased by automatically actuating thecontrollable valve 22. Thus, the mass flow through bypass fluid line 13decreases as can be seen from the diagram.

Thereby the heat exchange in the internal heat exchanger 6 is increased,which steers T2 back to the desired range R1 (indicated by dotted arrowA2′).

In both cases the mass flow is controlled proportionally so that nounsteady change in heat exchange occurs.

The mass flow through the bypass fluid 13 line is kept steady, if thetemperature measured by temperature sensor 23 remains c within thepredefined range R1.

Diagram b)

The fluid temperature and the pressure of the refrigerant of the coolingsystem are continuously measured the using a further temperature sensor15 and a pressure sensor 25 both of which are comprised by a fluid line12 between the second conduit 10 of the internal heat exchanger 6 andthe compressor 2. The further temperature sensor 15 and the pressuresensor 25 are located close to the inlet side of the compressor 2.

Based on the measurements of the further temperature sensor 15 and thepressure 25 an overheating of the fluid is continuously determiningusing controller 16. Controller 16 also controls the proportional threeway valve 22.

In diagram 5 b) the determined overheating OH1 on the inlet side of thecompressor 2 is, for example, shortly before exceeding a predefinedoverheating range R2 (indicated by solid arrow OA1). By way of examplethe overheating range can be 5 Kelvin to 15 Kelvin, with an optimaloverheating of 10 Kelvin in the middle.

Thus, the fluid mass flow through bypass fluid line 13 is increased byproportionally opening, controlled by controller 16, the controllablevalve 23 towards the bypass fluid line 13. Thereby the heat exchange inthe internal heat exchanger 6 is decreased, which steers OH1 back to thedesired range R2 (indicated by dotted arrow OA1′).

If an overheating OH2 of the fluid falls or is about to fall below thepredefined overheating range R2, which is indicated by solid arrow AO2,second control loops provides for proportionally reducing the fluid massflow through the bypass fluid line 13, which can be seen in diagram 5b). In other words, the controllable valve 22 is proportionally steeredtowards its closing position.

Thereby the heat exchange in the internal heat exchanger 6 is increased,which steers OH2 back to the desired range R2 (indicated by dotted arrowOA2′).

The mass flow through the bypass fluid 13 line can be kept steady, ifthe continuously determined or calculated overheating OH1, OH2 remains,for example, within the an (smaller) overheating range R2′ around theoptimal overheating point.

Thus, it becomes apparent that the second control loop acts as a secondsafety loop, which prevents fluid drops to enter the compressor 2 andthereby avoids a liquid hammer.

The first control loop represented in diagram a) generally overrules thesecond control loop represented in diagram b) the first control loopdominates.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Itwill be understood that changes and modifications may be made by thoseof ordinary skill within the scope of the following claims. Inparticular, the present invention covers further embodiments with anycombination of features from different embodiments described above andbelow. Additionally, statements made herein characterizing the inventionrefer to an embodiment of the invention and not necessarily allembodiments.

The terms used in the claims should be construed to have the broadestreasonable interpretation consistent with the foregoing description. Forexample, the use of the article “a” or “the” in introducing an elementshould not be interpreted as being exclusive of a plurality of elements.Likewise, the recitation of “or” should be interpreted as beinginclusive, such that the recitation of “A or B” is not exclusive of “Aand B,” unless it is clear from the context or the foregoing descriptionthat only one of A and B is intended. Further, the recitation of “atleast one of A, B and C” should be interpreted as one or more of a groupof elements consisting of A, B and C, and should not be interpreted asrequiring at least one of each of the listed elements A, B and C,regardless of whether A, B and C are related as categories or otherwise.Moreover, the recitation of “A, B and/or C” or “at least one of A, B orC” should be interpreted as including any singular entity from thelisted elements, e.g., A, any subset from the listed elements, e.g., Aand B, or the entire list of elements A, B and C.

LIST OF REFERENCE SIGNS

1, 20, 30 cooling system

2 compressor

3 condenser

4 expansion valve

5 evaporator

6 internal heat exchanger

7 first conduit

8, 9 line between condenser and expansion valve

10 second conduit

11, 12 line between evaporator and compressor

13 bypass fluid line

14 controllable valve

15 second temperature sensor

16 controller

17 fluid line between compressor and condenser

22 controllable valve

23 temperature sensor

25 pressure sensor

26 connecting flange

28 inlet junction

29 outlet junction

T1, T2 temperatures measured by temperature sensor 23

OH1, OH2 determined overheating

1. A cooling system, comprising: connected in a loop by fluid lines andin succession, a compressor, a condenser, an expansion valve and anevaporator; and an internal heat exchanger having a first conduit inheat exchanging contact with a second conduit, the first conduit beingpart of the fluid line between the condenser and the expansion valve andthe second conduit being part of the fluid line between the evaporatorand the compressor, wherein a bypass fluid line is arranged between twoends of the first conduit of the internal heat exchanger or extendsbetween one of the two ends of the first conduit and a position along alength of the first conduit.
 2. The cooling system according to claim 1,further comprising a controllable valve arranged in the bypass fluidline and being configured to control an amount of fluid flowing throughthe bypass fluid line.
 3. The cooling system according to claim 2,wherein the controllable valve comprises a three way valve and isarranged either at a junction of the bypass fluid line and the fluidline between the condenser and the internal heat exchanger or at ajunction of the bypass fluid line and the fluid line between theinternal heat exchanger and the expansion valve.
 4. The cooling systemaccording to claim 2, further comprising a temperature sensor arrangedin the fluid line between the compressor and the first conduit of theinternal heat exchanger and being configured to control the controllablevalve based on a temperature measured by the temperature sensor.
 5. Thecooling system according to claim 2, further comprising a temperaturesensor arranged in the fluid line between the second conduit of theinternal heat exchanger and the compressor, and a control deviceconnected to the temperature sensor and the controllable valve, thecontrol device being configured to control the controllable valve basedon a temperature measured by the temperature sensor.
 6. The coolingsystem according to claim 2, further comprising a pressure sensorarranged in the fluid line between the second conduit of the internalheat exchanger and the compressor.
 7. The cooling system according toclaim 4, wherein the temperature sensor arranged in the fluid linebetween the compressor and the first conduit of the internal heatexchanger is arranged between the compressor and the condenser.
 8. Thecooling system according to claim 1, wherein the bypass fluid linecontains only a single controllable valve and/or wherein an amount offluid flowing through the bypass fluid line is controlled only via asingle controllable valve.
 9. The cooling system according to claim 2,wherein the controllable valve comprises a proportional valve.
 10. Thecooling system according to claim 1, wherein a smallest diameter of thebypass fluid line is larger than a largest diameter of the fluid line,including the first conduit, between an inlet junction and an outletjunction, or wherein the smallest diameter of the fluid line, includingthe first conduit, between the inlet junction and the outlet junction islarger than a largest diameter of the bypass fluid line.
 11. The coolingsystem according to claim 1, wherein the condenser is free of abranch-off, wherein the first conduit of the internal heat exchanger andthe expansion valve are connected solely via the single fluid line, andwherein the fluid line between the condenser and the first conduit ofthe internal heat exchanger is permanently open.
 12. The cooling systemaccording to claim 2, wherein the controllable valve is integrated in aconnecting flange of the internal heat exchanger.
 13. The cooling systemaccording to claim 1, wherein the cooling system is filled with R134a orHFO1234yf as refrigerant.
 14. A method for controlling the coolingsystem according to claim 1, comprising the steps of: measuring, a fluidtemperature of a refrigerant of the cooling system using a temperaturesensor comprising a fluid line between the compressor and the condenser;and controlling, proportionally to the fluid temperature measured by thetemperature sensor, a mass flow of fluid passing through the internalheat exchanger by automatically actuating a controllable valve that isarranged to control an amount of fluid flowing through the bypass fluidline.
 15. The method according to claim 14, further comprising the stepsof: measuring, the fluid temperature and a pressure of the refrigerantof the cooling system using a further temperature sensor and a pressuresensor,. both of which comprise a fluid line between the second conduitof the internal heat exchanger and the compressor, the furthertemperature sensor and the pressure sensor being located close to ordirectly at an inlet side of the compressor; continuously determining orcalculating, based on measurements of the further temperature sensor anda pressure sensor and using a controller, an overheating of the fluid;proportionally increasing the fluid mass flow through the bypass fluidline if the overheating of the fluid exceeds or is about to exceed apredefined max overheating threshold or overheating range; and/orproportionally reducing the fluid mass flow through the bypass fluidline close or equal to zero if the overheating of the fluid falls or isabout to fall below the predefined max overheating threshold oroverheating range; and/or keeping the mass flow through the bypass fluidline steady, close or equal to zero if the continuously determined orcalculated overheating remains on the predefined overheating thresholdor within the predefined overheating range.
 16. The cooling systemaccording to claim 7, wherein the temperature sensor arranged in thefluid line between the compressor and the first conduit of the internalheat exchanger is arranged between the compressor and the condenserdirectly after or close to the compressor.
 17. The cooling systemaccording to claim 9, wherein the proportional valve comprises aproportional two-way valve.
 18. The method according to claim 14,wherein the measuring is continuous.
 19. The method according to claim14, wherein the temperature sensor is located close to or directly at anoutlet side of the compressor.
 20. The method according to claim 15,wherein the measuring is continuous.